1. Technical Field of the Invention
This invention is concerned with a cable-section termination fixture for connecting together two or more seismic streamer cable sections.
2. Description of the Prior Art
In marine seismic surveying, a plurality of hydrophones are enclosed in an elongated tubular plastic jacket and are towed through the water by a ship. Electrical signals from the hydrophones are transmitted to a recording apparatus, mounted on the towing ship, through electrical conductors that are also enclosed in the plastic jacket. Since the streamer cable may be two miles or more in length, the streamer cable is divided into sections each of which is two to three hundred feet long. Termination fixtures are secured to each end of the cable sections so that the sections and the electrical conductors can be suitably coupled together.
The jacket is made of a plastic material such as polyvinyl chloride. This material stretches as much as 400% when subjected to towing tension. Accordingly, steel stress members are threaded through the jacket and are anchored to the termination fixtures at each end of a cable section.
The streamer cable must have neutral buoyancy in the water so that it will stream at a desired depth. The cable is made neutrally bouyant by filling the cable jacket with a light hydrocarbon fluid such as kerosene. It is evident that the steel stress members add weight to the cable along with the weight due to the hydrophones and electrical conductors. Thus, the number of hydrophones and conductors that can be enclosed within a cable section is limited because of the additional weight of the steel stress members. The details of conventional cable-section construction and cable-section coupling techniques are well known to the art. For example, see U.S. Pat. Nos. 3,914,014 and 4,092,629, both of which are assigned to the assignee of this invention, and U.S. Pat. No. 3,376,948.
In an effort to reduce the cable weight, it has been proposed to replace the steel stress members by light-weight tapes made by braiding together fibers of a tough plastic material such as Kevlar made by Dupont Chemical Co. The tensile strength of this material is 400,000 psi, comparable with the tensile strength of steel stress members. In use, several such tapes are embedded longitudinally in the wall of the plastic jacket at the time when the jacket is extruded. At each end of a cable section, portions of the embedded tapes are exposed by stripping away some of the jacket. The exposed portions of the tapes are then bonded to the termination fixtures by a potting compound such as epoxy cement.
Although the resulting bond is mechanically satisfactory, once the bond is made, it can never be disassembled without destroying it; the epoxy bond is a permanent bond. Because the cemented bond is permanent, it is impossible to repair a defective cable section in the field.